The answer is lower frequency waves are associated with greater relaxation. To simplify, when researchers looked at electroencephalography patterns across a whole night’s sleep they noticed that lower frequency waves are associated with greater relaxation. In addition, when a person is wide-awake and alerts an electroencephalography will yield beta waves. The presence of spindles on an electroencephalography specifies the beginning of stage 4 of sleep and deep sleep is reflected to begin in stage 3 of sleep.